Polymerization of Phenylacetylenes with Rhodium Zwitterionic Complexes: Enhanced Catalytic Activity by π-Acidic Diene Ligands

Zwitterionic Rh catalysts bearing a series of tetrafluorobenzobarrelene (tfb) ligands proved to be highly active in the polymerization of phenylacetylenes. The highest catalytic activity for the polymerization of phenylacetylene was observed with (tfb)Rh+[(η6-Ph)BPh3] (1). Catalyst 1 displayed higher activity to produce higher molecular weight polymer than the conventional nbd analogue, (nbd)Rh+[(η6-Ph)BPh3] (5, nbd = 2,5-norbornadiene). In the case of other zwitterionic Rh catalysts bearing polymethylated tfb ligands [tfb-Me2, 2; tfb-Me3, 3; tfb-Me4, 4], the catalytic activity tended to decrease with increasing number of the incorporated methyl groups. Catalyst 1 also showed high activity in the polymerization of phenylacetylene derivatives irrespective of electron-donating or -withdrawing nature of ring-substituents of the monomers.